Abrasive articles commonly include one or more grinding aids, i.e. chemical compounds, typically inorganic compounds, which improve performance characteristics of abrasive products. Such performance characteristics include cut rate, coolness of cut, product wear, and product life.
Cryolite, calcium fluoride, or similar compounds including ammonium-based salts are often employed either by themselves or with other compounds to improve the performance of grinding wheel-type abrasive articles. For example, U.S. Pat. Nos. 2,022,893 and 2,110,630 and British Pat. No. 444,141 (accepted Mar. 16, 1936) disclose grinding wheels containing cryolite or other water insoluble fluoride substance having similar properties, such as calcium fluoride and apatite as a grinding aid. U.S. Pat. No. 2,308,983 describes abrasive articles such as grinding wheels, containing a fluoroborate, such as ammonium fluoroborate or an alkali metal fluoroborate, (e.g. sodium fluoroborate and potassium fluoroborate), with improved performance characteristics. U.S. Pat. No. 3,246,970 describes an abrasive article such as a grinding wheel with a grinding aid comprised of a mixture of iron sulfide and potassium aluminum fluoride.
Abrasive articles, such as grinding wheels, comprising potassium aluminum fluoride and a heavy metal phosphide or iron sulfate are disclosed in U.S. Pat. Nos. 3,032,404 and 3,246,970, respectively. U.S. Pat. No. 3,030,198 discloses an abrasive article, such as a grinding wheel, comprising potassium hexafluorophosphate.
It is known in the art that the presence of sulfur in stainless steel swarf makes the recovery of nickel from the swarf both expensive and difficult. U.S. Pat No. 2,952,529 discloses a sulfur-free resinoid bonded abrasive wheel comprising cryolite and ammonium chloride which offers stainless steel cut performance approximately equal to wheels containing sulfur or sulfide fillers. A sulfur-free resinoid bonded abrasive wheel containing cryolite, ammonium chloride, and chilled iron grit to improve heat resistance is taught in U.S. Pat. No. 2,949,351.
A grinding wheel comprising alkali metal or ammonium chloroferrate or alkali metal or ammonium chlorofluoroferrate as a grinding aid is disclosed in U.S. Pat. Nos. 4,263,016 and 4,310,148, respectively.
U.S. Pat. No. 4,500,325 discloses an abrasive article in the form of an abrasive disk comprising EQU A.sub.x Me.sub.y.sup.II Me.sub.z.sup.III Hal.sub.E .multidot.nB.sub.f C.sub.g Hal.mH.sub.2 O.multidot.oNH.sub.3,
wherein A is an alkali metal ion or ammonium ion; x is a number between 0 and 10; Me.sup.II is a bivalent metal ion, i.e. Mn, Ca, Mg, Zn, Sn, Cu, Co, or Ni; y is a number between 0 and 2; Me.sup.III is a trivalent metal ion, i.e. Al, B, or Ti; z is a number between 0 and 2; Hal represents a halogen; E is a number between 1 and 10; n is a number between 0 and 10; B is an alkali metal ion or ammonium; f is a number between 0 and 1; C represents bivalent element (e.g. Ca, Mg, Zn, Sn, or Mn); g is a number between 0 and 1; e is a number between 1 and 2; m is a number between 0 and 10; and o is a number between 0 and 10.
U.S. Pat. No. 4,877,420 teaches abrasive bodies such as grinding wheels or cutting wheels having halogen-containing compounds as a filler.
European Pat. Appl. No. 0 239 918 (published Oct. 7, 1987) discloses a composite grinding wheel having an abrasive rim containing superabrasive grits (e.g. diamond and cubic boron nitride), an active halide filler, and particulate silver.
Grinding wheels comprising anhydrides of strong inorganic acids or acid salts of strong inorganic acids further comprising alkali metals, alkaline earth metals or ammonium is described in U.S. Pat. No. 2,243,049.
U.S. Pat. No. 4,381,188 discloses an abrasive disk comprising abrasive grains, a bonding agent, and pellets, wherein the pellets further comprise a binding agent (including phenolic resin), a pulverulent filler, and ammonium chloride.
It is also known in the art to improve the cut rate of an coated abrasive article by incorporating selected inorganic fillers into its bond system. For example, U.S. Pat. No. 3,541,739 and U.K. Pat. No. 1,145,082 (published Mar. 12, 1969) describe a coated abrasive article oversized with a top coating of a reactive filler above the conventional size coating, wherein the filler comprises a metal halide selected from a simple alkali metal halide and complex halide derived from alkali metal halide wherein the element other than alkali metal halide is selected from aluminum, boron, silicon including, for example, alkali metal halides, such as sodium or potassium chloride or sodium or potassium bromide which may be used in conjunction with sodium or potassium aluminum hexafluoride or a metallic sulfide of iron or zinc.
Assignee acknowledges that coated abrasive product comprising alkali metal hydroxide catalyzed phenolic resin and ammonium fluoroborate was sold in the 1970's. The ammonium fluoroborate was an occasional contaminate in a potassium fluoroborate grinding aid which was present in the size or supersize layer of some coated abrasive products. The presence of the ammonium fluoroborate contaminate was not observed to affect the grinding performance of the abrasive products.
U.S. Pat. No. 3,833,346 discloses an externally applied grinding aid comprising a matrix which is softer than the cutting material and a halogen salt or the like, including NH.sub.4 Cl and NH.sub.4 BF.sub.4.
A cleaning pad impregnated with an acidic material having a pH below 4 in a one percent aqueous concentration, including ammonium chloride and ammonium acid phosphate is disclosed in U.S. Pat. No. 2,690,385.
Coated abrasive and three-dimensional, low density coated abrasive articles differ significantly from bonded abrasive articles such as grinding wheels or cutting wheels. For example, grinding wheels are typically formed as a relatively deep or thick (three-dimensional) structure of abrasive granules adhesively retained together in a wheel. In contrast, a coated abrasive article typically comprises a support member, abrasive granules, and one or more layers of a bond system which serve to bond the abrasive granules to the support member. A coated abrasive article may further comprise additional non-bonding layers such as, for example, a supersize. Furthermore, a coated abrasive article generally has a significantly higher ratio of bond system to abrasive granules than a grinding wheel.
A three-dimensional, low density abrasive article comprises a three-dimensional, low density web structure, abrasive granules, and a bond system which serves to bond the abrasive articles to the web structure. Like a coated abrasive, a three-dimensional, low density abrasive article generally has a significantly higher ratio of bond system to abrasive granules than a grinding wheel. Furthermore, a three-dimensional, low density abrasive article typically has a void volume within the range from about 85% to 95% whereas the void volume of a grinding wheel is usually substantially less than 85%.
The art does not disclose the use of the ammonium aluminum fluoride-based salts of the present invention as grinding aids for coated abrasive or three-dimensional, low density abrasive articles.